Top Grades in Extreme Conditions

Jobsite Issue Excavating company must effectively grade a 450,000-cubic-yard cut-and-fill project that features difficult terrain and soil conditions.

The Project A single-family housing development site topography in which the appraisal notes say most of the lots will slope downhill, sideways or both. The lots wind their way up a ridge along a main entry street, to the top, where the terrain is characterized by a series of high slopes, deep valleys and a ravine

In addition, the existing soils on the site created another challenge. Various soil types were present, including Spring Water Formation (ash), Boring Lava (solid rock) and Colluvial Soil (red, brown and gray clay). Trying to use these native soils as structural fill was challenging because of their inconsistencies.

Jobsite Solution Brian Clopton Excavating used a set-up that equipped a John Deere 850J dozer with a Topcon MC-A1 GPS rover mounted on a MCA-1 GPS antenna that works in tandem with one of two HiPer Lite+ base stations deployed on the south end of the ridge.

The dozer also utilizes 3DMC Full Automatic Control software, which interfaces with the hydraulics of the dozer. The dozer cab was outfitted with a 9168 3D Control Box and an MC2.5 Magnetic Mounted GPS Box and Slope Sensor.

Construction machines equipped similar to this are using Global Navigation Satellite System (GNSS) technology, which is automating grading and excavation.

To take full advantage of a GNSS machine-control system, the unit uses a "rover." This is a rugged antenna mounted to a shock-absorbing, vibration-damping pole and a receiver box mounted in a secure location on the machine. Satellites send positioning data to another antenna/receiver combination at a stationary base station. Positioning data is also sent to the rover on the machine. The stationary base and mobile rover work together to provide real-time kinetic (RTK) position information, revealing the machine's three-dimensional location on the site.

The software also compares the machine's position to the design grade at a given location. The design grade information was compiled via the use of the GNSS-including "roving" of the site. The data files are loaded into a machine-mounted control box via a compact "flash card." The control box updates positioning data and sends signals to the hydraulic valves. The blade is automatically positioned for elevation and slope.

Other sensors inform the control box of certain machine conditions; for example, dozers used by contractors such as Clopton are equipped with a slope (tilt) sensor on the blade to measure the cross-slope of the cutting edge. "Indicate systems" like Topcon's 3D systems provide visual guidance for machine operators, who manually control the machine to cut or fill to the desired grade.

On a project with so many cuts, fills and grade changes like this one, the software helps an operator determine where material is located on the jobsite and where it needs to be moved with the aid of a real-time, color-coded cut/fill mapping feature. The operator can select different colors-which can be displayed in darker colors to show large topographical variations - to indicate cut, fill and on grade areas on the control box. The software also allows the graphical layout to be saved as an as-built survey.

Challenge Addressed - Various Soil Conditions The difficult terrain is only one challenge. "The soil conditions here are really challenging," Clopton added, pointing to a cut alongside the street that revealed the cross-section of the soils. Below the top soil layer, the material had a gray tint.

"If you look, you can see an ash layer-it's about 2 feet thick," Clopton said. At this stage of the project, Clopton was filling with spoil piles that were created when pipe trenches had been excavated earlier.

"Throughout the winter, we put all of the underground pipe in and took all the dirt and stockpiled it up here; now we're drying it because it was wet coming out of the ground and when you stockpile it wet, it stays wet," said Clopton.

Upon completion, hard-surface runoff will be pumped to a holding pond at the bottom of the site, or into the nearby system of street gutters and catch basins.

Results The increased grading and excavating productivity that Quimby and his machine operators enjoy with the use of the GNSS was reflected in dollars for this project. The developers have effectively received a discount from the engineers by not having to have cuts and fills staked.

"That is a direct result of the use of this equipment," Clopton said. "It makes our work go faster and provides us with an edge in bidding, not having to have a grade checker."

Clopton referred to a nearby intersection that has been dug out of a slope so that the street could be paved. The GNSS proved particularly valuable in this area because this spot is characterized by a significant number of grade changes. "This intersection was where the [GNSS] really paid off," he commented

Compared with conventional site-preparation methods, "I would say our productivity has doubled," said Jeff Lybarger, the site foreman on these projects. "The system saves me time, it saves us money and it makes the developer happy because you get the job done on time. It's already paid for itself because you're saving money in staking and doing things once instead of twice."

"It is this type of a project with complex grades where control of materials, construction staking and productivity are recognized immediately and therefore maximum return on investment in this technology is realized," said Jeff Peterson, senior vice president of the PPI Group, a dealer of surveying and construction equipment with several operations in the Northwest, including Portland and Seattle. The PPI Group, Topcon Positioning Systems' Northwest distributor, is Brian Clopton Excavating's GNSS grading equipment provider.

Don Talend of Write Results Inc., West Dundee, Ill., is a print and e-content developer specializing in construction, technology and innovation.